Crop production is affected by numerous environmental factors. Attempts to improve crop yield under stress conditions by plant breeding have been largely unsuccessful, primarily due to the multigenic origin of the adaptive responses (Barkla et al. 1999, Adv Exp Med Biol 464:77-89). Consequently, an increasing amount of research has been dedicated to developing transgenic plants that show increased tolerance to various environmental stresses. For example, transgenic plants have been described having resistance to a broad range of plant pathogens (Stuiver and Custers, 2001, Nature 411:865-8; Melchers and Stuiver, 2000, Curr Opin Plant Biol 3:147-52; Rommens and Kishore, 2000, Curr Opin Biotechnol 11:120-5; and Mourgues et al. 1998, Trends Biotechnol 16:203-10). Transgenic plants displaying increased drought tolerance have also been described (Laporte et al. 2002, J Exp Bot 53:699-705; Qin et al. 2002, Plant Physiol 128:544-51; and Iuchi et al. 2001, Plant J 27:325-33).
Activation tagging in plants is a method of generating random mutations by insertion of a heterologous nucleic acid construct comprising regulatory sequences (e.g., an enhancer) into a plant genome. The regulatory sequences can act to enhance transcription of one or more native plant genes. Accordingly, activation tagging is a fruitful method for generating gain-of-function, generally dominant mutants (Hayashi et al., Science (1992) 258: 1350-1353; Weigel et al., Plant Physiology (2000) 122:1003-1013). The inserted construct provides a molecular tag for rapid identification of a native plant gene whose mis-expression causes a mutant phenotype of interest (e.g. drought tolerance or pathogen resistance).